>Important to whom? having localized readers every so often
>along roads and highways could efficiently gather the
>information which could be centralized (to whatever degree
>needed) over land lines or air as economical. Alternately,
>local sites could be primed to look for certain vehicles and
>relay information. This isn't that difficult to design or
>maintain economically.
>
>- samantha

I assume this system would be of great interest to any government that
wants to keep tabs on its subjects.

If the intent is to keep track of everything, for possible future evidence,
like the British seem to want to do with electronic communications, the
requirements quickly become immense. Tracking a few cars via onboard
transponders, once the infrastructure is in place, would be fairly simple.
The trouble with this being used to investigate criminal acts is that the
bad guys are going to fox the system - it's not hard to conceive of a black
market in "clean" transponders.

License plate recognition has been used in a few areas - I think Southern
California played with it, and New Jersey (?) was sending out mailings to
random people caught on film as a way of doing rush hour drive
studies. And then, there's Lo-Jack, which has caught a fair number of car
thieves.

Again, the system only works for law-abiding types, and stupid crooks.
Anyone planning something serious, like 9-11, will take this into account,
and will not be nailed by tracking devices.